Tapered conductor



May 12, 1953 T. amass ETAL 2,638,522

' TAPERED CONDUCTOR Original Filed March 9, 1944 5 Sheets-sheet 1 AC. If

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/ 80g /74 v 78 75' E 71 76 INVENTORS.

THOMAS B. GIBBS SAMUEL DINERSTEIN GEORG W- GILMAN BY l,

A T TOR/VF Y May 12, 1953 T. B. GIBBS EIAL TAPERED CONDUCTOR 5 Sheets-Sheet 2 Original Filed March 9, 1944 INVENTORsZ THOMAS B.GIBB5 SAMUEL DINERSIEIN GEORGE W. GILMAN HTTOE/VEY May 12, 1953 T. B. GIBBS EI'AL 2,638,522

TAPERED CONDUCTOR Original Filed March 9, 1944 5 Sheets-Sheet 5 INVENTORS.

THOMAS 8.61585 ma SAMUEL DINERSTElN GEORGE W.GIL,MAN

May 12, 1953 Original Filed March 9, 1944 ig-a j 190 5 Sheets-Sheet 4 ffO/I STANDARD z 477 FEIQ. GE/VIEAIU? A E I @/-ZO I I l z V i I INVENTORS.

THOMAS amass /66 SAMUEL DINERSTEIN 4 GEORGE W.GILMAN 205 A BY 8 l ATTORNEY Patented May 12, 1953 UNITED STATES PATENT OFFICE TAPERED CONDUCTOR tion of Delaware Original application March 9, 1944, Serial No. 525,764, now latent No. 2,605,218, dated July 29, 1952. Divided and this application May 17, 1951, Serial No. 226,778

(Cl. 20-1-- 6D) 11 Claims.

The present invention relates to improvements in tapered conductors, and this application is a division of application Serial No. 525,764, filed March 9, 1944, now Patent No. 2,605,218, which relates to Methods and Apparatus for the Manufacture of Tapered Conductors.

Tapered conductors such as referred to herein may be used. for various purposes, but an important use is in the manufacture of nonlinear r ieostats or potentiometers. By a nonlinear potentiometer is meant a, potentiometer in which equal movements 01' the slider from different starting positions result in unequal changes in resistance. Such potentiometers have been constructed by winding resistance wire on a tapered form, and potenticmeters constructed in this way .re satisfactory for some purposes. There are objections, however, such as difficulties in winding and the impossibility of obtaining a rapid increase the resistance per turn without unduly increasing the size of the potentiometer.

Nonlinear potentiometers have also been constructed by means of a tapered conductor which is made by splicing together short sections of resistance wire of different diameters. Utilizing this method, a tapered conductor is produced which tapers by stages, or step-wise from one end to the other. For a practical potentiometer,

"however, the number of steps must be rather large and the cost of splicing the numerous 'sec- 1 tions required is high. There are also winding difficulties. Hence, this method is not very successful.

The foregoing will make evident the need for a one piece tapered conductor, having desired characterties as to rate and degree of taper, adapting for use in the construction of nonlinear potentiomcters. This requirement is met by the present invention, which makes it possible to manufacture such conductors for the first time, so far as known.

According to the invention, a tapered conductor manufactured from a conductor of uniform section by subjecting the wire to anodic reduction in an electrolytic bath. The Wire is through the bath at a relatively high speed at first; and the taper is produced by gradually decreasing the speed, thereby progressively increasing the time in the bath and the amount of metal removed from the Wire. has the original diameter at one end and any desired diameter at the other end, with the understanding, of course, that a limitation will be imposed here by the minimum tensile strength requirements. in practice wire has been re- The resulting wire electrolyte.

duced from a diameter on th'e'order of tor 5 mils or larger to ;a diameter of .9 mil, which is about the smallest size of wire that has the necessary mechanical strength.

it may be pointed out, moreover, that by suitably varying "the rate at which the speed is changed, different forms of taper can be produced. Thus, tapers corresponding to various current and upon "the anode current efficiency.

The current tends to vary in accordance with the size of the-wire exposed to the action'of the bath, which becomes progressively smaller as the process continues. The anode current efficiency varies with :the temperature of the bath and the concentration of the electrolyte. Another problem is to obtain a bright, smooth finish on the wire, which requires a high current density and accurate control over the specific gravity of the Still another problem is to obtain a high enough current so that the process will not take an abnormally long time. The seriousness of this problem may be appreciated from the fact that the wire operated'on is resistance wire, having low conductivity, resulting in the fact that the current required for commercial operation of the process is many times-greater than the carrying capacity of the wire. A still further problem is introduced by the fact that although the resistance wire material has a fair tensile strength, many of the tapered wires which have to be made are extremely fine and are rather week at the small end, therefore. The strength of some of these fine wires is measured in ounces rather than in pounds. This makes it imposible to use any type of pulley system to guide the re repeatedly through the electrolytic bath. The force required to pull the Wire through a system of this kind would break the wire before the required reduction in diameter is obtained. The making of a, good electrical connection to the moving Wire is another problem, especially since any friction produced would increase the force required to move the Wire.

The foregoing and other problems are solved in a satisfactory manner by the present invention, as will be fully explained in the detailed specification. It may be pointed out at this time, however, that the problem of obtaining the required high anode current is solved by providing a large plurality of small electrolytic cells, arranged in a row, through which the wires are drawn on straight lines. are made to the wires on both sides of each cell, so that no part of any wire has to carry more than a small fraction of thetotal current. Compartments containing mercury are arranged alternately with the electrolytic cells for this purpose. The substantially frictionless nature of the sliding connections formed by the mercury, coupled with the fact that the wires move through the mercury compartments and the electrolytic cells on straight lines, makes the force required to move the wires very small.

It may also be mentioned at this time that the successful operation of the invention from the standpoint of producing tapered conductors with predetermined tapers, reproducible at will, is due in large part to the elimination of all variable factors which affect the rate of anodic reduction,

with the single exception of the time factor. The

time in the bath, depending on the rate at which 'the'wire is pulled through the bath, is rigidly controlled in accordance with the particular form of taper to be produced.

Proceeding now with the detailed explanation, the apparatus will first be described, reference being had to the accompanying drawings, in

Fig. 1 is a more or less diagrammatic view showing in elevation some of the principal parts of the electrolyte circulating system, including the main and auxiliary tanks;

Fig. 2 shows the electrolytic cell system in elevation, and also the arrangement for supporting the spools containing wire to be processed;

Fig. 3 is a plan view of the electrolytic cell system;

Fig. 4 is a cross section on the line 4-4, Fig. 2;

Fig. 5 shows the wire pulling mechanism in elevation;

Fig. 6 is a plan view of the same;

Figs. 7 and 8 show details of the take-up spools and their supporting arrangements;

Fig. 10 is a plan view, showing one of the electrolytic cells complete with an associated mercury compartment, substantially full size;

Fig. 11 is a section on the line iI--I I, Fig. 10; Fig. 12 is a section on the line I2I 2, Fig. 10; Fig. 13 is a section on the line I3--I3, Fig. 10;

Fig. 14 is a supplementary drawing showing the Y arrangement for guiding the processed wires onto the take-up spools; and

Fig. 15 is a diagrammatic layout of a tapered wire.

Figs. 1, 2, and 5, when properly arranged, show the complete apparatus in elevation. In order to connect these drawings, the sheets bearing Figs.

1 and 5 should be placed upright, with the sheet bearing Fig. 2 between them and on its side; and the sheets should be adjusted so that the broken parts of the bench, table, or base It are in alignment. When the sheets are thus arranged the drawings show the electrolytic cell system, Fig. 2, in the center, with the electrolyte supply on the left, Fig. 1, and the wire pulling mechanism on the right, Fig. 5. The wires or conductors being processed are carried on the spools such as I43, Fig. 2, and are pulled through the electrolytic cells from left to right by means of the transfer or take-up spools such as I68, Fig. 5,

Electrical connections all) 4 It will be convenient to describe the electrolytic cell system first, reference being had to Figs. 2, 3,

,and 4, and also to the detail drawings Figs. 10 to 13, inclusive.

The reference character I il indicates the top of a bench, table or other support, referred to hereinafter as a base, which is conveniently located about 3 or 4 feet above the floor so that the parts mounted on the base will be readily accessible to the operator. The base may be of wood or any suitable material.

Theelectrolytic cells are supported upon two parallel spaced strips II and I2, which are held in position a short distance above the base It by means of a number of brackets such as I3 and M, Fig. 4, and I4 and I5, Fig. 2. These strips may also be of wood, and together with the base III, are preferably given a coating of acidproof paint. The cells are arranged on the two strips I I and !2 in a row extending parallel to the strips as shown in Figs. 2 and 3, and each cell rests partly on strip I I and partly on strip I2, bridging the space between them, as seen clearly in Fig. 4.

The number of electrolytic cells is variable, but there should be a considerable number of them. There may be, for example, 16 complete electrolytic cells, of which only a few are shown in Figs. 2 and 3. Each cell is made in two sections, which may be referred to as cathode and electrical contact sections, respectively. The cathode and elec trical contact sections alternate in the cell assembly. Thus, the sections I6, I8, 20, etc. are electrical contact sections, while sections i'I, I9, etc. are cathode sections. The sections I6 and I! may be regarded as constituting the first electrolytic cell, sections I8 and I9, the second, and so on.

Due to the arrangement of the cells in a compact row, however, the cathode section of each cell has adjacent thereto on the right the electrical contact section of the next cell, that is, each cathode section is between two electrical contact sections, the last electrical contact section 23 being added to carry out the arrangement. From a functional standpoint, therefore, each complete electrolytic cell may be regarded as being composed of a cathode section and two electrical contact sections. Considered on this basis, the sections I6, I1, and I8 constitute the first cell, sec

tions I8, I9, and 28, the second, and sections ill,

22, and 23, the last, each electrical contact section except the end sections it and 23 being common to two cells.

Before going any further into the cell asscm bly it will be well to explain the structure of the individual cell sections, reference being had to Figs. 10 to 13, inclusive, which show the electrical contact section I8 and the cathode section I9.' The electrical contact sections are all like section I8 and the cathode sections are all like section I9, so it will be sufiicient to describe these two sections.

Thesections may be made of various materials and may be constructed in various ways. Acidproof material should be used, or the cells should be coated with acidproof paint. A convenient material to use is polystyrene, which is not attacked by the acids of which the elsetrolyte is composed. The sections shown are made from solid blocks of polystyrene by machining and drilling operations.

The electrical contact section It has a plurality of cavities or compartments, separated by partitions, whereas the cathode section I9 has only a single compartment. The partitions and maniacs.

5. the walls of the cathode TSQGtiOlI arerslottedzto receive the conductors being processedamt consequently the compartments-whichcontain.:.water or electrolyte are not: leakprooii. Certain of the compartments are. providedtotakecare of the leakage problem which thus arises. This will all be fully explained.

Considerin the cathode section 19,.there isa single rectangular compartment 24;. for" electtrolyte, having the. slotted endiwa'lls Land, 26. There are four slots such as and28 each end wall. The width of the. slotsshould belt-1st slightly greater than the. diameter of the largest wire to be processed and may'.O-l2 inch, for or ample, or 12 mils. The depth or the slots is about one-half the height Of'the walls: as will. be clear from the showing of slot 21, Fig. 11.

Electrolyte is supplieclto the'compartment 2:6 through a nipple so, which is set'intoan-opcning 32, 13, communicating with the bore 3| extending 1engrlnvisev through the cathode sectic-n 18 as indicated by the dotted lines in Fig. 11. The bore 3! is intersected by'the crossbore 33, Figs. ll and 13, the endof whiohis closed by the plug 34. This cross bore. supplies elecwith the four conductorv slots such .as 21in the wall 25 of the compartment 24.

There are two overflow tubes, indioatedat 39 and 45 Figs. 10 and 12. These tubes are set in holes drilled in the bottom of the; compartment 26 to closed by the plug 42. The drain-pipe 43 is inserted in another hole which is drilled up through the bottom to intersect the cross bore 4!.

The nipple 32, nozzles 3 --33, plugs 3.4- and 42, and tubes Ml, and 43 are preferabdy made of pol styr ne. Before assembly the contacting ces are painted with a cement made by dissolving polystyrene in a suitable organic solvent. The solvent evaporates after the parts areassembled and leaves themfirmly'attaehed to-the main block. of which the cathode section is fabricated.

The longitudinal bore 3! in thecathode section is is in alignment with similar bores in all the other sections, and thcsebores, therefore; form a continuous conduit extending through the complete cell assembly. The conduit is closed at both ends by polystyrene plugs, or the-bores-may be omitted from the end sections it and 23. Electrolyte is supplied to the conduit.v by means of a number of tubes which connect with nipples such as 3% as will shortly be explained. The direction of how through the cathode section is be traced at this time,,however. The electrolyte passes from the conduit (bore 31). to the cross bore. 33, and from the cross bore it is supplied to the compartment 24 by the four nozzles ti -3i". The compartment 24 is maintained full of electrolyte up to the top of the overflow tubes 38 and l the surplus passing down these tubes to the cross bore 4| from which it is drained on through the drain pipe 43. The collection of the electrolyte from the drain pipes such as 43 and its return to the circulating system-willbe explained later.

Each nozzle has a single rather meet the cross bore 41, the endoi which is aster 44;, 10 and comprises a. horizontalsec, tion' lr'ai, which rests; on thebottom of thecompertinent 24, a. vertical section 46 which extends upward out of the compartment, and a short lwrizontalzsection 41 which extends partly over the rear wall of the compartment. The cathode inshown in Figs. 10, 1,1, and 12 but the shape thereof is" best seen in Fig: 12. The cathode is preferably made of a specialgraphite which is sold under the; trademark Kai-bate." This material is very dense, having a porosity of less thanil and has relatively high heat and elec-- trical conductivity as compared to other forms of carbon. The section 410i the cathode should be copper plated so. that aconductor can be soldered. on, as indicated in Fig. 3. Then the sections 4-1; and are coated with acidproof paint so that only the section 46 will be efiectivelyin contact with electrolyte.

Considering the electrical contact section It; now-the first compartment 48 at the left is an electrolyte collecting compartment and is provided to collect the electrolyte that leaks through thcslotted wall-2d of the adjacent cathode section [1. The electrolyte is drained off as fast as it is collected through the hole to inthe bottom of the compartment, which connects with the drain pipe Fig. 11.

A low partition 5| separates compartment 48 from the second compartment 5-2, which is a water collecting compartment, provided; to collect the. water which leaks through the slotted. partition 55. A hole 53in th bottom of compartment 52 connects with the drain pipe 54 and drains ofi the water as fast as it is collected.

Tothe right of the partition 55 is the washing compartment 55, which is provided with an overflow tube 57, set in a hole drilled through the bottom of the compartment. At the opposite end of the'hole-the; drain pipe 55-5 is inserted.

The next compartment is the mercury compartment, formed by the partitions 5B and 62. This compartment is recessed at the bottom to receive a rod-6c, made preferably 01 some metal such as molybdenum which is a fairly good condoctor. and is not readily attached by mercury. The terminal screw 63 passes through a hole drilledin the. front wall of the compartment 59 and is threaded into a tapped hole in the end of rod 60. The rod so is drawn up against the Wall ofthecompartment by means of a nut 64, a washer 66 being interposed to seal the opening if desired; although this-is not strictly necessary. A second nutM is'provided to enable a conductor to be connected to the terminal screw 53.

The. compartment 59 is filled with mercury up to a short distance, below the top of partition 58, or well above the'bottcms of the slots in the various partitions andwalls which receive the conductors being processed. These conductors pass through the mercury, therefore, which is provided in order to make a good sliding connection to the moving-conductors from the terminal 53. The rod 80 is provided in order to make the re-- sist-ance between the terminal and the several conductors substantially the same.

The memory does not leak out of compartment 55' through the slots in'the partitions Stand. 52, due to the narrow width of the slots and to the fact that the mercury does not wet the polystye rene of which the partitions are composed nor the conductors being processed. The surface tension of the mercury, therefore, prevents its escape'through the slots in the partitions.

Water is continuously supplied to the mercury compartment 59iby an arrangement. which; will be described shortly. -The water overflows the partition 58 and fills the washing compartment 56-up to the top of the overflow-tube 51', through which it drains off.

To the right of the mercury compartment 50 there are two compartments 01 and 69 which are separated by the low partition 68. Compartment 61' is provided to collect the water which leaks through the slotted partition 62 while compartment 69 is for collecting the electrolyte that leaks through the slotted wall 26 of the electrolyte compartment 24 of the adjacent cathode section I9. The compartments El and 60 have holes drilled in the bottom in which there are inserted the drainage pipes I and II.

The various tubes or pipes of the electrical contact section I0, such as 50, 54, etc. are attached by means of polystyrene cement, as in the case of the cathode section I9. It will be understood of course that the sections themselves are secured together in the same way. When as sembled and cemented together the sections become firmly united and the structure is as rigid and strong as if fabricated from one continuous block of polystyrene.

The main electrolyte tank is indicated at I3, Fig. 1, and is supported on a suitable sub-base I6 by means of brackets such as M and 15, the arrangement being such that the tank I3 is below the level of the base ID. The tank l3 may be made of any suitable material. It may be made of sheet steel, for example, and in this case is coated with acidproof paint.

Suitable means is provided for heating the tank 13, shown as comprising a Bunsen burner 'I'I.

' The supply of gas to the burner is controlled by means of a manually operated valve 19 and an electromagnetically operated valve 30. The reference numeral 18 indicates a heavy metal plate secured to the bottom of the tank to distribute the heat from the burner.

In addition to the main electrolyte tank 13 there is an auxiliary tank 8|, which is supported about 3 feet above the base I0 in any suitable manner,as by means of an uprightmember 82.

The electrolyte is transferred from the main tank I3 to the auxiliary tank 8| by means of a centrifugal pump 83, driven by the motor 84. The pump 83 may be of known construction,- adapted for pumping acid. The casing and impellor may be made of polystyrene, for example,

and the shaft of stainless steel.

The electrolyte flows from the pump 83 to the tank BI through a hose connection 85. Rubber hose may be used here, as it is for other connec-- tions to be described. The tank 8! is maintained full of electrolyte to the top of the overflow pipe 86, and supplies electrolyte to the electrolytic cells, as will be described. The excess overflows through the pipe 86 and passes by way of the hose connections 01' and 89 to the vessel 90, containing :a hydrometer 90'. A constant level in the vessel 90 is maintained by the overflow connection 9|, through which the excess electrolyte returns to the main tank "I3. The Y connection 88 and the short hose 92, open at the upper end. are provided in order to get rid of air entrapped in the overflow from the tank 8| and thus avoid an excess of bubbles in the vessel 90, which would otherwise interfere with the reading of :thehydrometer.

The electrolyte is delivered by gravity from the tank BI through the hose 93 to the electrolytic cells in Fig. 2. For this purpose a plurality of T connections such as 94 may be provided, together with short pieces of hose such as 95, by

means'ofr which: connections are made with the nipples such as 30; Thus themain supply hose 03 is connected with the channel or conduit BI in the electrolytic'cell system at a plurality of points, tending to equalize the pressure at all the cells.

The wash water is supplied to the electrolytic cell system through a :pipe I03, which is connected to the water supply system through a hose connection I04 anda valve I05. The pipe I03 is supported onthe strip II by means of brackets such as I06, as shown in Fig.4, and is equipped with av plurality of nozzles such as I01, I08, etc., one for each electrical contact, by means of which water is delivered to the mercury compartments of such sections. The water pressure may be regulated by the valve I05 and should be sufficient to maintain a good circulation through the washing compartments such as 56.

The arrangement for collecting the electrolyte and wash water from the electrolytic cell system may now be described. Referring to Figs. 2 and 4, it will be seen that two troughs 96 and 91 are provided, which are supported on the base III by means of blocks such as I00 and which extend beneath and parallel to the electrolytic cell system. The troughs are so disposed that all the drain pipes such as 50', 50, II, 43, etc, which carry electrolyte, empty into the trough 96, whereas the drain pipes such as 54, 54, BI, 10, etc., which carry water, empty into the trough 91. The trough has an outlet pipe 98 .and a hose connection IllI, by means of which the electrolyte collecting in the trough is drained back to the main tank I3. The trough 91 has an outlet pipe 90 and a hose connection I02, by means of which the water collecting in the trough is disposed of.

Returning now to Fig. 1, it was mentioned that the main tank 13 is heated by suitable means such as the Bunsen burner H. The flow of gas to the burner is adjusted by means of the valve 79 so that the burner is adapted to maintain the electrolyte at a temperature which is somewhat higher than the desired or optimumqtemperature and means is provided to cool the electrolyte whenever its temperature rises slightly above the desired value. The cooling means comprises one or more coils of glass tubing H0. Water is supplied to the tubing I I0 through a hand valve I I3, an electromagnetically operated valve I I2, and a hose connection III. The hose connection H4 leads to the waste pipe or drain.

The valve H3 is open when the apparatus is in operation and the admission of water to the cooling coil H0 is controlled by the valve H2, which in turn is controlled by the relay I I3. The relay circuit includes conductors I I4 and H5 which lead to a thermally operated switch H0 which is immersed in the electrolyte in the main tank, When the temperature of the electrolyte rises to a predetermined point which is slightly higher than the desired temperature the switch II6 closes the circuit of relay II3 and the relay energizes. The operation of the relay closes a circuit for the electromagnetically operated valve II2, which thereupon opens, starting the flow of water through the coil I I0. The-rise in the temperature of the electrolyte is thus arrested and it shortly begins to fall, with the result that the switch I I6 opens; the relay I I3 is deenergized, and the valve I I2 is closed again.

Fig. 1' also shows the power leads II! and H8, which may be connected to any convenient A. C.

outlet. From these leads current is supplied to ampe e 9. the motor 84, relay H3 and the electromagnetically operated valves 80 and H2. A switch IIQ controls the circuit of the motor 84 and the circuit of valve 80. Another switch IZG is in the circuits of relay I I3 and valve H2.

The electrical connections to the electrolytic cells may now be explained. Two bus bars are provided, which may be made of copper tubing, and are attached in suitable manner to the outside edges of the strips II and I2. They extend throughout the length of the electrolytic cell assembly. All the cathodes are connected in parallel to the bus bar I2I by means of short conductors such as I23, which are soldered to the cathodes and to the bus bar. All the terminals such as 53 are connected in a similar manner to the bus bar I22.

Power for the electrolytic cells may be supplied by a motor generator set, of which only the generator I is shown. As indicated, the generator I25 is a shunt wound, direct current generator, with field rheostat. The negative and positive output leads from the generator terminate in a double pole double throw switch I, which in one position connects the generator to an artificial load comprising the resistance I32 and rheostat I33, and in the other position connects-the generator to the conductors I35 and I36, which are connected to the bus bars I2i and I22 respectively. Associated with the positive side of the circuit there are a plurality of current regulating devices each of which is provided with an individual switch such as iii. Six of these devices are preferably of two ampere capacity, while the seventh is of one ampere capacity. An ammeter I28 is connected in the negative side or the circuit. A high shunt resistance I29, in series with the rheostat I39, provides for a fine adjustment of the output.

The conductors or wires to be processed are wound on spools from which they are drawn off during the processing operation. Fig. 2 shows four spools Ht, i-lI, I42 and I43 carrying four wires I56, iEI, I52 and 453, respectively, which have been connectec up preparatoryto pulling them through the electrolytic cell system.

The spools Hit-4 53 are carried on a diagonally disposed cross member I which is secured to a vertical support Hi4 mounted on the base Ill. The spools are rotatable to permit the wires to be drawn off, but rotation of the spools is opposed by individual friction brakes in order to keep the wires taut. There is a U-shaped bracket I56 which is suitably attached to the 'crossmember I525. The spool I43 is carried on a shaft I41 which is rotatable in bearings formed by semicircular notches out in the ends of the two legs of bracket hit. The shaft Ifil has an enlarged central portion which at one end is a little larger than the hole the spool, being made with a slight taper, however, so that the spool can readily be pressed onto the shaft by hand or removed therefrom. The pulley I43 is fixedto the shaft i-il and supports a weight I49 by means of a cord 254. Teen the spool is rotated by drawing on the wire 553, the shaft I41 and pulley I48 rotate with it, the rotation being opposed by the weighted cord which slips in the pulley groove. Weights of different sizes may be provided, and

they are preferably slotted like scale weights so that they can readily be changed to vary the braking effect.

After leaving the spools Mil-I43, the wires I5i)I53 pass beneath the grooved rod I56 before entering the electrolytic cell system. This rodis supported on base I 0 by means of the bracket I55. Rod I 56 is not shown in the plan view, Fig. 3, but is similar to the grooved rod I58. The function of the rod I56 is to guide the wires properly into the electrolytic cell system, and for this purpose the grooves are spaced the same as the slots in the various partitions, while the rod is supported at the correct elevation to hold the wires at the bottom of the slots.

The grooved rod I58, supported on bracket I51, performs a similar function at the other end of the electrolytic cell system. The rods I56 and IE8 can be supported for rotation if desired, but this is not necessary provided they are made of some hard, smooth material. Ihey may be made of glass, for example.

After leaving the electrolytic cell system, Figs. 2 and 3, the wires I50-.I53 pass to the take-up spools loft-I68 on the wire pulling mechanism, Figs. 5 and 6, .there being, however, an intervening grooved guide rod I'GI, Fig. 14, which will presently be described. The wire pulling mechanism will be described next.

This apparatus is mounted on a metal plate I it which rests on the base Ill, and consists essentially of two oppositely disposed rotatable cones HI and Il2, a motor E18 for driving the first cone i'ii, an axially movable wheel I87 for coupling the two cones Ill and lit, and suitable gearing by means of which the second cone I72 drives the take-up spools lib-I69 at a variable speed clelizirmined by the position of the coupling wheel The motor I'I9 may be a split phase synchronous motor and is mounted on a support I97 which rests on the plate H6. The motor may be operated on commercial alternating current, supplied through a switch I98, but preferably a standard frequency generator is provided to run the motor, as indicated in the drawing, in order to avoid speed variations due to changes in frequency. The motor speed may be 1860 R. P. M.

The cone i'II may be of any suitable material, such as aluminum, for example, and is supported on a shaft I13 which is rotatable in bearings provided at the upper ends of the supports I15 and I76. These supports rest on and are secured to the plate Ill The motor 1 l8 drives the cone I II by means of a worm I fixed to the motor shaft and a worm wheel IBI fixed to the shaft I73. The gear ratio may be 1 to 18, for example, in which case the speed of the cone will be 100 R. P. M.

The cone I12 is similar to the cone Ill and is mounted on a shaft It' l, which is rotatable in bearings with which the supports ill and H8 are provided.

The second cone I72 is driven from the first cone IiI by means of an axially movable wheel I8'i, as previously mentioned. The wheel I8? is supported on a sliding carrier comprising the two some members I84 and I85 which are rigidly clamped to the two spacers I86 and I99, the former of which is drilled and tapped to receive the lead. screw I82. A tubular sleeve 2% is rigidly secured to the side members kid and I85 of the carrier, as by a drive fit, and is slida'ble on the fixed shaft I83. The wheel It? is preferably a rubber tire mounted on a hub 25H which is rotatable on the sleeve 2B0, suitable washers being interposed between the hub and the side members I84 and I85 as indicated. The shaft I83 is socured to and supported on two upright standards I 83 and I89 whichare mounted in spaced relatlon on the plate I III. The lead screw I82 is pro vided with bearings at the upper ends of these standards, andis adapted to be rotated by means of the hand wheel I9 I. A counter I90 is mounted on the standard I83, is connected to the lead screw, and functions to indicate the instant position of the carrier or wheel I81, as measured by rotations of the lead screw.

It will be seen that by rotating the hand wheel I9I in one direction or the other the carrier and the wheel I81 can be traversed in either direction along the fixed shaft I03. By rotating the hand wheel in a clockwise direction, for example, the carrier can be moved to the right until the wheel I81 engages the cone H! where it has the largest diameter and at the same time engages the cone I12 where it has the smallest diameter. The counter I90 should be so related to the lead screw that it reads zero in this position of the wheel I81. By rotating the hand wheel I9I in the opposite direction the carrier stood that the hand wheel I9I cannot be operated unless the cones are rotating.

The shaft I14 on which cone E12 is mounted drives a countershaft I94 by means of a worm I92 and worm wheel I93, and the said countershaft drives the shaft 202 by means of the spur gears I95 and I96. These gears may be secured to their respective shafts by means of set screws, so that they may be changed if it should become necessary to shift the speed range up or down. The shaft I94 is rotatably mounted on a suitable support 203. The shaft 202 is rotatably mounted on a movable supporting block 204 so that the distance between the centers of shafts 202 and I94 can be changed if made necessary by a change of gears. This construction is shown in Figs. 7 and 8. The block 204, which supports shaft 202, is carried on a support 205 to which it is pivoted by means of a pin 206. The support 205 includes a vertically disposed slotted member 201. The block 204 is secured in position by means of a clamping screw 200, which lies in the slot in member 201 and is threaded into a tapped hole in the block 204. The clamping screw 208 may conveniently be provided with a knurled head 209. It will be seen that when the screw is loosened up the block can be rotated to right or left on the pivot pin 206, Fig. 8, and can then be secured in the desired position by tightening the clamping screw.

The take-up spools I65IB8 are mounted on the shaft 202 as shown. There is a disc 2I0 secured to the shaft 202 and the spools I65-l60 are clamped against this disc by means of a wing nut 2II. The construction of the spools will appear clearly from Fig. '1, which shows two of them in section. They may be molded from suitable plastic material. Describing the spool !65 briefly, it has a winding space bounded by two flanges, of which the flange at the left is several times higher than the other. The wire being processed, such as wire I50, is wound on from left to right, starting next to the higher flange, and the end of the wire is attached to the spool by inserting it in a notch in the flange and bending it back. The circumference of the winding space should have some convenient value, to facilitate relating the number of feet of wire on the spool to the number of turns, and may be exactly one foot, for example. The spool has to be rotatably mounted when the wire is drawn off in the winding operation and to this end is provided with a bearing sleeve 2l3.

The spools l65-IBO are all alike and it will be understood that a considerable number of them will be provided in order to permit continuous operation of the apparatus. When four tapered conductors have been made and wound on the spools 55-468, the spools are removed and are replaced by four empty spools.

The reference character 2I2 indicates a counter, which is suitably mounted on top of the block 204. The counter is actuated by a pin on the gear I96, as indicated in Fig. 7, and counts the number of rotations of the spools hit-I00. Since the spools are one foot in circumference the counter will indicate the number of feet of wire on the spools at any stage.

Fig. 14 shows the arrangement for feeding the wires onto the spools NBS-I68 as they leave the electrolytic cells. A grooved rod IBI is provided, and is supported on two L-shaped members I59 and I60, which are fastened to the base I0. The grooves on the rod I0! have the same spacing as the spools E05I63. The rod i0! is axially movable. At the start of a processing operation, the rod is in the position in which it is shown in the drawing, where it is held by the spring I02. As the operation proceeds and the wires are wound up on the spools, the rod i0! is moved longitudinally to the right by turning the wing nut I00 once in a while. Thus the wires are prevented from piling up on the spools and are wound on in single layers. It is important that the wire be wound on in a single layer, because it is desirable to draw the wire off the spool in the way that it is wound on, that is, large end first. A single layer also ensures that the counter 2I2 will accurately indicate the number of feet of wire drawn through the cell system. I

It will be in order now to discuss the gear ratios employed at the wire pulling mechanism, particularly the variable ratio between the speeds of the cones HI and I12, with a view to making clear the different wire speeds that may be obtained.

It has been mentioned before that the speed of motor I19 is 1800 R. P. M. and that the ratio of the motor speed to that of the first cone I1I is 1:8 to l. The speed of the cone, therefore, is R. P. M. The ratio of the diameter of the cone I1I at its larger end to its diameter at the smaller end may be l to 1, and since cone I12 is the same, it follows that with the wheel I81 in its extreme right hand position (counter at zero) the driving ratio between the cones is 4 to 1. Cone I'l2, therefore, rotates at a speed of 400 R. P. M. As regards the drive from the cone I12 to the shaft 202, the gear ratio I92-I93 is 25 to 1, while the gear ratio mil-496 is 10 to 3. The speed of countershaft I0i, therefore, is 16 R. P. M. and the speed of shaft 202 is 4.8 R. P. M., or .08 R. P. S. Now since the circumference of the spools carried on the shaft 202 is exactly 1 foot, the linear speed of the wire when it is drawn through the electrolytic cells and wound up on the spools will be .08 foot per second, or 12.5 seconds per foot. This is the maximum wire speed with the apparatus described.

The minimum speed of the wire can be calculated in the same way from the minimum speed ofthe cone H12, which is 25 R. P. M., and

which Szzspeed of cone in S=s, eed of cone Hi dzdiaineter of cone Ill at the point of drive d'zdiameter of cone H2 at the point of drive If we substitute in the above equation the value 106 for S and the values i and 1, respectively, for d d, and solve for S, we obtain ace as the speed or" the cone H2, which checks with the veluc previously given. Substituting other vs of d and d corresponding to various interine e settings of the lead screw as indicated :ounter 1% and solving for S we may ascertain the speeds of cone 112 which resuit termediate settings of the lead screw in the tails below. From the cone speeds wire speeds for the same lead screw settings can be calculated and such values are also included in the table.

3 v w Cone S ecd, Wire Snead. Leno So) .u Settin R. sec. 5 Ft.

The above table is incomplete, but will suffice for the purposes of this explanation. A complete table or chart may beprepared on the same plan, showing the wire speeds in seconds per foot for all the lead screw settings from O to 160, inclusive. This table may be used in determining the proper lead screw settings which are required to produce any desired speeds, as will-shortly be more fully explained.

It should be noted that although the values given for the cone speeds and wire speeds'are theoretically correct, the actual values may differ slightly, due to the fact that the drive wheel 887 between the two cones must have an appreciable width and that the point of drive does not always coincide with the exact center of the wheel. This may cause slight variations in the values or" d and d for any particular lead screw setting. These variations seem to average out to some extent and are not serious. It may be stated that a table of wire speeds prepared by timing with a stop watch checks quite closely with the table prepared from the calculated values. a

If desired a curve may be prepared in which the values for wire speed are plotted against the settings of the lead screw, By means of the curve the proper lead screw setting for any required wire speed may readily be determined.

sch intermediate settings. The values "14 The electrolyte used is a mixture of crtho phosphoric I acid and sulphuric acid: and preferablyhas the following composition.

Parts H'sPO'i 300 H2304 6U H2O ..s 60

In-the above formula, the proportions are given by volume. vThesuhihuric acid is concentrated, while the phosphoric acid is concentrated, that is, it contains 15% of'water.

The quantity of electrolyte should be relatively large as compared to the capacity of the electrolytic cells. For theapparat-us shown the circulating system should holdfive gallons or more of electrolyte.

Generally speaking, the invention is adapted for the processing of any kind of wire, although the electrolyte might have to be modified in certain cases. When liquid mercury is used dor making the electricalconnections to the wires, however, as in the apparatus disclosed herein, only wirewhich does not amalgamate readily can be used. That is, the composition of the wire must be such that it is not wet by the mercury. Fortunately for the manufacture of r-heostats and potentiometers suitable resistance wire which is not readily attacked by mercury is available. The resistance wire known as "Nichrome-maylbe used, for example. Another resistance-wire which has been used successfully has the following composition:

I Resistance wire'of the above composition" has a specific resistivity of about SOO ohmsper circular mil foot, has a low te'mperature coehicient, and a fairly high tcnsile'strength.

The apparatus described, with l2- mil slots, will handle wire up to about 10 =mi ls in diameter. The slots could be made larger to take larger wire, but there is a limit in this direction imposed-by the excessive leakage of water and electrolyte that would occur. The'necessity of avoiding loss of mercury also imposes a limit on the size cr" the slots.

Before processing, the wire should be given a treatment known asde'passivation, the object of which is to prepare the wire for the anodictreatment in the electrolyticcells. Unless the wire is depassivatedfithe anodic reaction does not start promptly at all pointson the surf-ace'of thewire when current is applied, and somewhat irregular and uncertain results are obtained.

Iniorder to facilitate the'depassivation treatmentthe wire should be wound on'the spools such as I43, in spacedcoils, with the coils in adjacent layers crossing each other in a kind of basket weave pattern, thus producing an open winding which is readily penetratedby the depassivating agent. The spools such as I43 should have ribbed or fi-uted winding spaces and should be made of material which is not attacked by acids.

The spools carrying the wire to be depassivated are first dipped in a cleaning solution such as is commonly used: in electroplating processes, inorder to make the wire chemically clean. The wire is then rinsed in water and is given a cyanide dip in order to remove any traces of the chemicalcl'e'a'ner' that may remain. After rinsing once more, the wire is immersed in hydrochloric acid for about thirty seconds and is then rinsed and dried. This completes the depassivation treatment. The treatment is effective for only a day or two and consequently the wire should not be depassivated until shortly before it is to be used, preferably on the same day, or the day before.

The operation of the apparatus in the manufacture of tapered conductors may now be explained. For this purpose it will be assumed that the apparatus is installed as described, and is to be started up for the first time, or is being started up after a shut down.

The main tank I3 is first filled with electrolyte of the hereinbefore stated composition. The electrolyte should almost completely fill the tank, as the loss of electrolyte to the rest of the system when the circulation is started will reduce the electrolyte in the tank to a safe working level, as indicated by the dotted line.

The switch I I9 is now closed in order to start the motor 84, which drives the pump 83. The operation of the pump transfers electrolyte from the main tank I3 to the auxiliary tank 8i through the hose connection 85. The electrolyte in tank 8! immediately starts to drain out by way of the hose connection 93 to the cathode sections of the electrolytic cells, filling all the compartments such as 24, Fig. 11, with electrolyte up to the tops of the overflow tubes such as 39 and 40. {is electrolyte continues to be supplied it overflows through the tubes such as 39 and 40 in each cathode compartment and is collected in the trough 90, whence it returns to the main tank I3 by wayv of the hose connection llll. Thus the circulation Qof electrolyte through the cathode compartments of the electrolytic cells is established and maintained. The pump supplies electrolyte to the auxiliary tank 8| faster than it can circulate through the electrolytic cells and the tank soon fills, therefore, the excess draining off through the overflow pipe 86 and hose connections 8'! and 89 to the vessel 90, containing the hydrometer 90, which isalso filled and drains into the main tank I3 by way of the hose connection 9! The wash water may now be turned on by opening the valve I05, which supplies water to the pipe I03, which in turn supplies water to'the nozzles such as I01 and I08. Each nozzle 'directs a stream of water onto the mercury in the associated mercury compartment such as 59, Fig. 11, and fills the compartment, the wateroverfiowing the partition such as 58 to the washing com.- partment such as 56, whence it overflows through a pipe such as 51 to the collection trough 91. From the collecting trough the water is allowed to run to waste through the hose connection I02. As mentioned before, there is some leakage of electrolyte through the slots such as 2? and 28 in the walls of the cathode compartments and there is also a leakage of water through the slots in the partitions such as and 62. The leakage electrolyte is collected in the compartments such as 48 and 69, whence it drains into the collecting trough 96, while the leakage water is collected in the compartments such as 52 and 61, whence it drains into the collecting trough 91. Thus the electrolyte and wash water "circulating systems are kept entirely separate, notwithstand-' ing the fact that they both leak.

The next operation is to turn on the supply of cooling water to the main tank 13 at valve H3. The switch I20 in the circuit of the electromag- I6 netic valve I I2 canbe closed at this time also. The valve remains closed, however, for its circuit is open at contacts of the relay H3. No cooling water is supplied to the tank, therefore, for the present.

When the switch H9 was closed it completed a circuit for the electromagnetic valve 88 and this valve accordingly opened. The gas may, therefore, be turned on at valve 19 and the burner 11 may be lighted. The heating of the electrolyte in the main tank 13 is thus started. The gas may be turned on full at the start in order to lose as little time as possible.

When the temperature of the electrolyte reaches about 46 C. the gas supply to the burner ii is adjusted so that only a slight amount of excess heat is supplied to the tank. The heat supplied must be suificient to produce a rise in the temperature of the electrolyte, but at a slow rate, so as to avoid waste of gas.

The thermal switch H6 is set to close at 47 C. When the temperature of the electrolyte reaches this value, therefore, the switch operates and closes a circuit for relay H3. Upon energizing, the relay I I3 closes a circuit for the electromagnetic valve H2, which now opens and admits cooling water to the coil H0 in the main tank I3. This stops the rise in the temperature of the electrolyte, which shortly begins to cool. The switch H6 then opens, relay H3 is cleanergized, and the valve H2 is closed. The cooling operation as described above is repeated as often as required, depending largely upon the adjustment of the burner I1, and the arrangement iseffective to maintain the temperature of the electrolyte within close limits.

The system will operate with the electrolyte at other temperatures than the one given above, provided the temperature is maintained constant. The reason why a variation in temperature is objectionable is that anodic reduction like electroplating, effects a smaller actual transfer of metal than might be expected from theoretical calculations. In other words, the anode current efficiency is considerable less than 100%. The efficiency changes with changes in temperature, and, therefore, the temperature should be kept constant in order to eliminate this variable factor that would otherwise be present. Since the anode current efiiciency increases with an increase in temperature, it is desirable to operate at a fairly high temperature. If the temperature is too high, however, disadvantages appear, such as excessive loss of water by evaporation. It has been found that very satisfactory results are secured if the temperature is maintained constant at some value which is about 46 C. or 47 C.

The density of the electrolyte should now be checked by means of the hydrometer 90'. It is found that good results are obtained if the specific gravity is maintained at about 1.600. The specific gravity is important as affecting the finish on the processed wire, a bright, smooth finish being obtained only if the specific gravity is maintained Within a certain range. This range appears to have wider limits with higher temperatures, which is another reason for operating with the electrolyte at a fairly high temperature. So far as the finish is concerned, therefore, some variation from the stated value of 1.600 would bepermissible, but the specific gravity also afiects the anode current efiiciency and hence should be held as close as possible to the value selected. The principal change that occurs in the specific gravity is due to the loss of water by evapora- .lytic cell system.

tion. The hydrometers hould be observed fre quently and water added when required.

The operator may now close the switch I98, Fig. 6, to start the motor H9. The cones Ill and I12 are thus set in rotation and the hand wheel IQI may be rotated to set the counter I96 to zero. This operation moves the drive wheel 18 to its extreme right hand position,' in which the cone [72 rotates at maximum speed. The switch I88 is now opened to stop the m'otor H9.

If not already done, four tal reeup spools such as ISL-H38 may now be placed on the shaft 202, where they are clamped in positionby man er the wing nut 2! I, as shown in Fig. ii.

Four spools such as Mil- I43 containing depassivated wire may now be mounted as shown in Fig. 2. The end of wire L50 is then passed under the grooved rods I56 and 158, Big. 2, and the grooved rod IGI, Fig. 14, and is attached to the high left hand flange on the take-up spool [55, Figs. 6 and 14. The portion of the wire w h e end wee th r ov d reds 5 and 153 may simply rest on top of the electrolytic cells for the present. The other wires lfil, I92

and I53are attached to spools {-56, I 6 1' and 168,

respectively, in the same manner.

The operator should now adjust the wires properly in their respective grooves in the rods {55, 1,58 and i6 l, and will then ,see ,to it that the wires enter their respective slots ,inthe various partitions and compartment wallsofthe electro- The wiresmay be guided into their slots and pressed downby .handand will readily fall intothe proper positions. The .relation of the wires to the other parts of the electrolytic cell system may be seen from Fig. 2, and also from Fig. 11, which shows theportion of wire 152 which extends through the .electrical contact sectioniS andcathode section). All four wires. are also-se'en-in theplanviewFig. .3, except 'theguide rod 156 to the guide rod. L58. .The force required to pull them-throughgthej cells is, 7 therefore, .very small, as previously mentioned. .In fact, practically the-only force required is that which isnecessary to ,ovcrcomethefriction at the brakes onthespools i. 4 0 -j-l 3. ,Thebrake friction should be just sufilcienttqkeep thewires taut.

:The, motor generator ,set which includes the D.= 0. nerator. .13 new be. starte an Las .soon as the generator volta e .i bu l u 1 th switch l34'may beclosedto its upper position.

The resistances I32 and 133 ,constitute V an artifi i l a w ic has previQi l x be n. adi sts t take app ox mat h .sam urren as h electrolytic cellv system. Enough of, theeurrent insu at n de e suc a 2 ar ne cut-in by n ea-ns ,oi switches, such as I21 .tQ- 95. the dfifii fid amount of current which in theease of, ,theap- 1 jsaiefalisesbntes hereirrwith; four wires being FQQ EQ emultansqu i abo tlmmpe A acc e a u me o h cur en ca b mad vl xr ans otth h shs hu resi ance-.12

and the rheostat I30.

The factors havingabearing onthe selection of the proper current valueifmay. be discussed briefly at this point,

The current-density, referring to thecurrent density at the anodes in the electrolytic cells, which'are constituted by the wires being processed, should be as high as possible. One obvious reason for this is that the higher the current density the faster the anodic reduction. Another reason is that a fairly high current density is necessary in order to secure a bright, smooth finish on the wire. The current density is limited by the current carrying capacity of the wires, however, and should not be so high as to unduly heat the wires,'which are in contact with the cell walls and partitions at the slots. The polystyrene of which the parts are made becomes soft at a rather low temperature.

' N ow the characteristic of the wire which determines the'current density is its surface area, whereas the current carrying capacity or conductivity is determined by its cross section, other things being equal. Since as we increase the size of the wire the cross section increases faster than the surface area, the larger the wire the higher the permissible current density.

The current value of 13 amperes is a value which has been found experimentally to be satisfactory in the described apparatus for processing the fine wire, the smallest diameter of which is on the order of 1 mil. This amount of current does not raise the temperature of the wires beyond a safe point and at the same time it results in a sufficient anodecurrent density to give a bright, smooth finish on wires up to 4 or 5 mils in diameter, or slightly larger.

"It will be appreciated, however, that as the size of the'wire is increased the current density will decrease, with the same total current, and will eventually become so low as to afiect the finish on the wire. For wires having a larger minimum diameter than about 2 or 3 mils a considerably higher current value could be selected, and may be required. Whatevervalue is selected it should be kept constant, if wires having a desired predetermined taper are to be made. It should be borne in mind that in this discussion reference is being made to the apparatus disclosed, comprising sixteen cathode compartments and adapted to-process four wires simultaneously. If the number of cells is increased, or the number of Wires, the total current must be increased in proportion in order to obtain the same current density.

Th statement that the current should be kept constant, of course, is in conformity with the preferred method of operation, in which all factors afiecting the rate of anodic reduction are kept constant, except the time. By varying only the time factor the method is simplified and has been found to be suitable for the production of a considerable variety of tapers. It isrecognized, however, that twoor more different current values could be used, each on a different section of the wire, and each being kept constant while it is in use. For example, a current value ,of 25 amperes could be used on the larger half of the wire and a current value of 13 amperes on the smaller half. This procedure would complicate the process somewhat, but itwould speed it up, and might be necessary in certain cases to give sufiicient current density to produce a bright finish at the large end of the wire.

Continuing with the description, the apparatus is now ready for the processing of the four wires ISO-I53 which have been connected up, it being assumed that sumcient time has elapsed since the switching on of the artificial load to permit the Amperites I28 to-warm up and attain a accdtaiz constant current carrying capacity. The operator may accordingly throw the switch I34 to its lower position, thereby disconnecting the generator I from theartil l'cial load and connecting it to the bus bars I21 and I22 of the electrolytic cell system. 7

Current now starts to flow through the electrolyti'c cells and the anodic reduction of the Wires begins. A't thi's time the operator also hoses the switch we 'to start the motor n9, thus setting the spools -168 in rotation and beginning to pull the wires I5B-I53 through the electrolytic cell system by winding them up on the. spools. The counter I90 having been set at zero, the linear wire speed is 12.5 seconds per foot.

The electrolytic cell system is approximately seven feet long, measuring from the point where the wires enter the first cathode section to the point where they leave the last cathode section. and accordingly it takes 87.5 seconds (7x125) for the seven foot sections of wire which were in the electrolytic cell system at the start of the operation to be pulled entirely through. It will be assumed now that the operator allows a few more feet of the wires to be pulled through and then stops the operation by switching the generator 125 back on to the artificial load and by stopping the motor lid. The operator can tell when to do this by observingthe counter 2I2,

which preferably was set to zero before motor I19 was started.

It should be stated that the foregoing assumption as to the procedure followed by the operator is based on the further assumption that the operator has no information as to the constants of the apparatus; that is, he does not know the wire speed which is required in order to produce the desired taper on the wires. He will naturally have to investigate this phase of the matter before he is able to produce any complete tapered wires having desired characteristics as to length and rate of taper. The resistance wires under consideration may be anywhere from 30 to 100 feet long, or many times. longer than the electrolytic cell system.

The wire I53 may now be cut off where it: leaves the eectrolytic cell system, and the winding thereof on the spool 38 is completed by hand,

the end being attached to the spool in any suitable manner, with a piece of tape, for example, or by engaging it in a notch in the right hand flange of the spool. This spool is then removed. The other wires l52l50 are then cut off one after the other, the unwound portions are wound up on their respective spools, the ends are attached to the spools to prevent unwinding, and the spools are successively removed.

We now have four test wires, each about fifteen or twenty feet long, which have been processed as described and wound up on individual spools. Each of these wires includes three parts, a. section which was beyond the electrolytic cell system and attached to the associated take-up spool when the operation started, a seven foot section which was in the electrolytic cell system when the operation started, and which has been drawn out, and a third section which has been drawn in and out of the electrolytic cell system, or entirely through it.

Before explaining how these test wires are used, it will be advisable to go over the operation again and consider more in detail how it has affected the three sections above referred to.

Considering wire I53, for example, the first section thereof which extended between the electrolytic cell system and the take-up spool is 20 obviously unaffected by the operation, being merely wound up on the spool.

The next section, the seven foot section, is in the electrolytic cell system when the operation starts, and successive portions of it from right to left are subjected for progressively longer times to the action of the electrolyte as th section is drawn out. It is to be expected, therefore, that this seven foot section will be tapered from the original diameter at the right to a smaller diameter at the left.

In order to explain more in detail the nature of the taper and how it is produced, the seven foot section may be considered as being made up of subsections l, 3, 5, 7, etc., which were in the cathode sections at the time the operation was started, and subsections 2, 4, 6, etc., which were located in the anode sections at that time. The subsections are numbered from right to left, as the apparatus appears in Fig. 2.

Let us first consider the effect that is produced on the wire by its motion to the right for a distance sumcient to pull the odd numbered subsections of the wire, which were located in the cathode sections at the start, entirely out of such subsections. This distance is approximately 2%; inches in the apparatus shown herein.

Subsection No. i was in the last cathode section 22, and is progressively reduced in diameter from right to left, as it is drawn out of the cathode section. That this is true will be evident from the fact that successive parts of the wire from right to left are subjected for progressively longer times to the action of the electrolyte.

Simultaneously with the tapering of subsection No. i, as described above, identical tapers are produced at all the other odd numbered sub sections as the result of their being pulled out of their respective cathode sections.

The movement of the wire which was sufficient to pull the No. I subsection out of the last cathode section was, of course, effective to pull an equivalent length of the No. 2 subsection into such cathode section, producing a taper which is complementary to that produced on the No. l subsection. That is, the taper is reversed.

The same effect is produced at all the other even numbered subsections, 4, 6, etc., as they are drawn into the associated cathode sections next adjacent on the right. Each such even numbered subsection is given a reverse taper.

The anode sections are somewhat longer than the cathode sections, that.is, the space between two cathode compartments is somewhat longer than the length of a compartment, and consequently at this time there will be a portion of the No. 2 subsection which has not yet entered the associated cathode section. The same is true of the other even numbered subsections.

Consider now the effect after the wire has moved to the right a little farther, or just sufficient to cause the left hand end of the No. 2 subsection to enter the cathode section. This movement of the wire causes a part of the No. 2 subsection to pass out of the cathode section, and is effective to move the taper along the wire from right to left, the part of the subsection which passes out of the cathode section being reduced to a cylindrical formation. Again the effect is the same at the other even numbered subsections,

We may next consider the effect which is produced by the further movement of the Wire to the right far enough to pullthe No. 2 subsection entirely out of the last cathode section 22, such movement causing the No. 3 subsection to be drawn into said cathode section. The No. 2- subsection has its contour changed to that of a cylinder throughout its length, for it has been pulled entirely through the cathode section and all points on its surface have been subjected to the action of the electrolyte for equal periods of time. The No. 3 subsection, which was tapered by being drawn out of the cathode section in which it was located at thestart, is reduced to a cylinder also, for the effect produced by pulling it out. of one cathode section and into another is the same as that produced by pulling it. into and out of thesame cathode. section.

It will be clear that the effect produced on the remaining odd numbered subsections is the same; that is, these subsections are all. reduced to cylinders. Since the even numbered subsections also have a cylindrical formation. at. this time, the entire seven foot section we are considering, or rather that part of it which still. remains in the electrolytic cell system, will be cylindrical in form, as it was before the operation started. Its. diameter has been reduced, however.

We may consider next the result which is produced by the further movement of the. wire to the right far enough to entirely withdraw the No. 3. subsection from. the last cathode section 22, such movement also causing. the No. 4 subsection to enter the cathode section.

From what has already been said it. will be clear that the N0. 3 subsection is. tapered as it is. drawn out. of the. cathode section. The taper is. similar to that which was produced on subsection No. l, but it will be understood that the largest diameter of the tapered subsection No. 3

It. will be unnecessary to continue farther with this. detailedv analysis. Itwill be clear that the complete seven foot section of wire, after it has been drawn entirely out of the. electrolytic cell system, will be made. up of. sixteen, tapered subsections, or the same number of subsections as. there are cathode sections, and fifteen cylindrical subsections. The first tapered subsection will have its. largest diameter equal to that of the unprocessed. wire, and each ofthe. remaining tapered subsections will havea larger diameter which is equal to the. smaller diameter of the nexttapered subsection to the right. The cylindrical subsections which join the tapered subsections. will progressively decrease in diameter from right tovlift.

For practical purposes these cylindrical subsections. may be neglected and the seven foot sectionmay be considered as having a continuous taper from one end. to the other. As a matter of fact the number of subsections, is great enough so that the points where the contour of the wire changes from tapered to-cylindrical: can scarcely be detected.

Asregards the remainder of wire I53, the section whch is pulled through the electrolytic. cell system following the sevenfoot section, it will be clear thatthis third section willhave the form of a. cylinder, the diameter of which is equal to the smaller diameter of the tapered seven foot section. That this is true will be evident from the fact that all partsof the third sectionare pulled entirely through the electrolytic cellsys- =tem and are subject to the action of the electrolyte for equal periods of time:

The test wire 153 as thusproduced; therefore, comprises anend-section several feet long, which 22* has not been subjected to the actin of the. elec trolyte and which has its original diameter, a middle section seven feet, long which may be regarded as being continuously tapered, and another untapered or cylindrical end section several feet long which is of reduced diameter.

The operator may now proceedto ascertain the diameter of the seven foot tapered section ot wire I53 at its smaller end. The diameter at the other end, of course, is that of the original wire, which presumably is known. The smaller di ameter is equal to the diameter of the smaller and section and is determined in any suitable manner. One method which is, well adapted for. use in. connection with these small resistance wires is to measure the resistance of a carefully measured length of the end section and calculate the diameter from the result obtained and the known resistance of the material per circular mil foot.

Measurements may be made on the, other three. test wires in the same way. The results should be. the same, or approximately the same. If the diameters thus determined are notsubstantially the same, the reason for the discrepancy should, of course, be-found and-corrected andadditional test wires should, be prepared. Improper 1613551- sivation might-be the. source of trouble. Assuming that the results on the four wires check, the average of the tour diameters thus; determined may be taken as the true diameter.

From this point on it, will be convenient to-con tinue the explanation with reference to Fig. 12, which illustratesthe method of producing; a resistance wire comprising a cylindricalend section having a diameter of (ii, a tapered section 21 feet long having a diameter ch at one end and a diam eter at; at the other end, and another cylindrical end section having a diameter d4- It will be assumed that this is the particular resistancewire that is to be made. The drawing also shows one of the test wires in superimposed relation, comprising a tapered section 7 feet long-andthe two cylindrical end sections as shown. As to this test wire, it will be assumed that the diameter of the tapered section at the smaller end, as determined by the measurements justv described, is (is.

A little consideration now will show that the test wire is not sufficiently tapered. Its diameter at the left hand end of the tapered section is d5, whereas the diameter of the desired resistance wire at the corresponding point is (12.

The operator accordingly is advised'that the time occupied in producing the taperedsection of the test wire'was insufiicient. That is, the wire was drawn out of the electrolytic cell system in too short a time for the requisite amount of metal tube removed; The correct time can. be=deter mined by comparison of the volume of metal actually removed with the volume of metal which has-to. be removed in order to produce. the required taper, the volume of metal removed being directly proportional to the time.

Suppose we let V0 be thevolume of metal removed from the seven foot tapered sectionof the test wire to reduce its diameter at the. small end to (is, and let V1 represent the volume of metal which must be removed inorder to. reduce. the diameter to do instead of do. These volumes can readily be calculated.

Assuming that the volumes V6 and- V1 have been calculated, we can letto equal the time required-to produce'the taper actually produced on the test wire, that is, the timerequired-to remove the volumevo, and let t1 equalthetimerequired 2eto produce the requiredtaperq or the time required to remove volume V1. Then to I t1=Vo 2 V1 .of the desired resistance wires, and consideration may be given to what further information will have to be obtained in order to carry out the operation successfully.

The resistance wire as depicted in Fig. 15 has a tapered portion which is 21 feet long, consisting of three seven foot sections, indicated as sections -I 2, and 3.

Sect. I is the section that is in the electrolytic cell system when the operation starts. From the calculation already made it has been determined that if this section is pulled out in time 151 the desired taper will be produced, that is, the tapered section will have a larger diameter equal to 111 and a smaller diameter equal to d2.

When sect. I is pulled out of the electrolytic cell system, sect. 2 is pulled in and will become tapered as indicated by the dotted lines 300. If sect. 2 is now drawn out at the same wire speed its contour will be reduced to that of a cylinder as indicated by the dotted lines Sill. Sect. 2 should not be cylindrical, however, but should be tapered from a large diameter of d2 to a smaller diameter of d3. It will be evident that in order to produce this taper an additional volume of metal equal to V2 will have to be removed.

Volume V2 can be calculated, like volume V1 was calculated, and will be slightly smaller than the latter volume. Time t1, or the time required to remove volume V1, has already been calculated. Then if t2 is the time required to remove volume V2,

Substituting the known values and solving for t2, the time in seconds may be obtained as in the case of ii.

We may now let T1 equal the total time required to pull out sect. I and T2 the total time required to pull out sect. 2. Then it will be evident that the following are true:

T1=t1 T2 t1+t2 Suppose now that sect. 2 has been pulled out of the electrolytic cell system in time T2 and has been tapered from the larger diameter of d2 down 1 to the smaller diameter of :23. sect. 3 was drawn into the electrolytic cell system ,and was tapered as indicated by the dotted lines :"302. Now if sect. 3 is pulled out of the electro- At the same time,

' 24 required to elapse in pulling out sect. 3, and can write the equation I T3 ti+ 2+i The times T1," I" 2, and T3 having been calculated, each of these values may be divided by 7 in order to obtain the corresponding wire speeds. The wire speeds may be represented by S1, S2, and S3. The operator may now refer to the table or curve which shows the relation between the wire speeds and lead screw settings and the lead screw settings corresponding to the wire speeds S1, S2, and S3 may be determined and noted down.

Having completed the calculations described in the foregoing, the operator is 'now ready to proceed.

The first thing to do is to start the motor I!!! to set the cones Ill and H2 in rotation. The hand wheel I9I may now be rotated in order to give the lead screw I 82 the proper. setting to produce a wire speed equal to S1. The correct setting has previously been determined, as explained, and is made by turning the hand wheel until the counter I shows the proper number of turns. The lead screw setting having been completed, the operator will stop the motor I19.

Four empty take-up spools such as I 65-I68 may now be placed on the shaft 262, where they are secured in place by the wing nut. The counter 2 I 2 is set to zero.

The operator may then out 01f the wires I5IlIEi3 just to the left of the point where they enter the electrolytic cell system. The parts of the wires which have been drawn into the electrolytic cell system are lifted out and discarded. The ends of the wires on spools I40-I43 are then passed beneath the guide rods and are attached to the take-up spools as previously described. As before, the wires are properly located in the grooves of the guide rods and are pushed down into the slots in the cell partitions.

Everything being ready now, and the operator having checked the current to make sure it is the same as before, the switch I3 is again thrown to its lower position. The generator I25 is thus again connected to the bus bars I2 I. and I22 and current starts to flow through the electrolytic cell system. The switch I98 is also closed at this time, starting motor I19, and initiating the rotation of the take-up spools to pull the four wires through the electrolytic cell system.

One of these wires may be assumed to be the wire shown in Fig. 15. Sect. I of this wire is the section which is located in the electrolytic cell system at the start and is pulled out at a speed which is equal to S1, calculated as previously described. It follows, therefore, that the section is drawn out in time T1 and will become tapered from a diameter of d1 at the larger and to a diameter of (12 at the smaller end.

As the operation proceeds the counter 2I2 counts the number of rotations of the take-up spools and indicates the number of feet of wire drawn out of the electrolytic cell system at any instant. The operator watches the counter 2I2 and as soon as sect. I has been entirely drawn out, as indicated by the counter, he quickly changes the lead screw setting to the previously noted setting which corresponds to wire speed S2. This can be done in a couple of seconds'and is timed as accurately as possible to coincide with the time the end of sect. I leaves the last electrolytic cell.

Sect. 2 is now pulled out of the electrolytic cell system at the wire speed S2, and in time T2, whereby it istapered from the diameterof d2 at the larger end to the diameter of da at the smallerend.

As the end of sect. 2 leaves the electrolytic cell system the operator quickly changes the lead screw setting again, this time to the previously noted setting which corresponds to the wire speed S3.

Sect. 3 is accordingly drawn out of the electrolytic cell system at the wire speed S3, and in time T3, and is tapered from the diameter of (13 at the larger end of the diameter of di at the smaller end.

When the end of sect. 3 leaves the electrolytic cell system the operator will note the fact, counter in indicating that 21 feet of wire have been drawn out, but makes no further change in the wire speed. The wire continues to be pulled out at the speed S3, therefore, and a cylindrical end section is formed having the diameter d4. When this end section is long enough the operator will stop the operation by reversing switch [3 6 and opening switch I98.

The four wires are now out off just to the right of the electrolytic cell system, the unwound portions are wound up on the respective take-up spools and the spools are removed, all as previously described.

Four tapered wires have now been produced, each comprising a cylindrical end section having a diameter of (ii, a section 21 feet long which tapers from a diameter of til at the larger end to a diameter of til at the smaller end, and a cylindrical end section having a diameter of (14. These wires should conform to specifications, provided the operations have been carried out as described.

The operator may proceed now to make four more tapered resistance wires in the same man ner. In this connection it should be noted that the lead screw setting must be changed first to the proper setting corresponding to speed S 1, since the cones Ill and 112 have to be in rotation when the change is made. It should be noted also that the sections of wire which were in the electrolytic cell system when the preceding four Wires were completed have to be cut off and discarded, if the described procedure is followed.

The treatment of the tapering theory in the foregoing explanation has been general, with a view to promoting an understanding of how the taper is produced, and the principles involved in predetennining the wire speeds and lead screw settings which are necessary to produce such tapers as may be required.

In this connection it will be understood that the directions given are applicable to any size of wire within the capacity of the apparatus, the wire size being limited only by the size of the slots. With 12 mil slots wire up to about mils in diameter may be handled, and the size of the slots could be increased somewhat. It will be understood also that the directions are applicable to the manufacture of resistance wires of any desired length, although the length should be some multiple of the length of the electrolytic cell system, which in the case of the apparatus described is approximately '7 feet. Fig. :15 shows an exaggerated taper, which would reduce the wire to zero diameter if prolonged through another '7 foot section, but this is a rather extreme case. As a rule much longer wires are required, comprising from '5 to 1.2 or more sec" 'tions and inv such wires the slope of the taper is correspondingly reduced.

As regards the form of the taper 'it will be evident from an inspection of Fig. 15 that the taper there shown is a conical or straight line taper, when considered from the standpoint of the decreasing wire diameters d1, d2, ds, and d4. In other words, a curve constructed by plotting the successively decreasing section end diameters against the corresponding distances measured along the wire is a straight line. The case is difierent if considered from the standpoint of the decreasing cross section of the wire, since the cross section at any point is proportionate to the square of the diameter at that point. A curve constructed by plotting successively decreasing cross sections against the corresponding distances is an exponential curve defined by an equation of the second order.

In the manufacture of tapered wires for potentiometers the resistance curve is of primary interest. Since the resistance of a wire is directly proportionate to its cross section, the resistance curve will be of the same type as the cross section curve. Hence the resistance curve of the tapered wire shown in Fig. 15 will be a second order of square curve.

If it is desired to make a resistance wire having a straight line resistance curve, then the cross sections at the ends of the seven foot sections can be computed from the resistance curve and from the values thus obtained the corresponding diameters can be calculated. These diameters can then be used to calculate the wire speeds in the manner already explained. Following the same procedure resistance wires having other types of resistance curves can be made.

In order to give a more definite idea of what may be expected in the practice of the invention, especially as to the time valuesinvolved, the data used in the manufacture of a representative resistance wire with the apparatus disclosed herein will now be given.

The resistance wire selected for this purpose is made of the alloy previously referred to herein and has an overall length .of about 49 or 50 feet. including a central tapered section having a length of 35 feet. The diameter of the original wire and the diameter of the tapered section at the larger end is 4.9 mils. The taper is conical, with slope of .1000 mil per foot, andaccordingly the diameter of the tapered section at the smaller end is 1.4 mils.

The table below gives the data tor the manufacture of the above wire, it being understood that four wires are made at the same time, and that the values for total current, electrolyte den vsity and electrolyte temperature are as previously recommended herein.

Section Feet T S L 0-7 201,. 88 28. 8 49 .7-14 383. 57 54. 8 86 14-21 545. 07 7-7. 8 '2l'28 686. 39 98 l i119 2835 807. 52 115. 3 128 In the above table the meaning of the entries in the first two columns will be obvious. The values of Tfgiven in the third column are inseconds and are calculated as already explained. Each entry in this column shows the total time T that should elapse while the corresponding section is being drawn out of the electrolytic cell system. {lilac-values of Sin the fourth column are the wire speeds in seconds per foot andare obtained by dividing the corresponding values of T by W. The values of L in the fifth column are the lead screw settings in turns, as indicated by the counter, and are obtained from a curve such as has been previously mentioned, which was made by plotting the lead screw settings against the corresponding wire speeds.

, In the manufacture of the wire the operator makes use of only the entrie in the last column. The initial lead screw setting is 49, and accordingly sect. I of the wire is pulled out of the electrolytic cell system at awire speed of 28.8 seconds per foot and in a total time of 201.88 seconds, The operator keeps track of the sections bymeans of the counter 2|2 :and as the end of the first section leaves the electrolytic cell system, or is about to leave, he changes the lead screw setting from 49 to 86, with the result that sectLZ is pulled out at a wire speed of 54.8 seconds per foot and in a total time of 383.57 seconds. The operation proceeds in this manner, with lead screw settings of 105, 119 and 128 as sections 3,, 4, and 5, respectively, are pulled out.

The last lead screw setting remains unchanged while the cylindrical section at the end is pulled out. The end sections are not shown in the table.

The total time required in the electrolytic cell system may be found by adding up the values of Tin column 3 of the table, including an additional entry equal to the last entry to take care of the smaller end section, and will be found to be a little more than 57 minutes. The time required for other resistance wires is in proportion to the amount of metal that has to be removed.

The output of the apparatus in making this specific resistance wire is about four wires per hour. The output can readily be increased by increasing the capacity of the machine, which can easily be arranged to handle more wires at a time.

While the procedure explained in the foregoing gives excellent results, a possible objection, if it can be referred to as such, is that the accurate timing of the changes in lead screw settings is interfered with to some extent by the impossibility of making such changes instantaneously. The time required to make a change is very small in. comparison with the time required to pull a seven foot section through the electrolytic cells, and consequently the operation is not critical, but a chance for some'slight irregularity does exist, especially if the changes in lead screw settings are made manually as described.

v A procedure which may be adopted to facili- .tate timing and to minimize the effect of an occasional inaccuracy consistsin making the first change in the lead screw setting after six feet of wire have been pulled out and in changing the setting every three feet thereafter, the changes being proportionately-smaller than those which would be required if made only every seven the apparatus inherently turns outseven foot sections each having a straight line resistance curve,

whic'hi's eminently suited to the manufacture of 'multi-section wires having the same type of resistance curve. This characteristic of the apparatus, however, makes it somewhat less suitable a c'onica1 taper or resistance wires having re for the manufacture of resistance wires havin V, 28 ance curves which are not straight lines. This is not to say that satisfactory wires having such tapers cannot be made in this way, for the taper is corrected every seven feet and the departure within each section is generally too small to be material, especially if the wire contains a considerable number of sections. In case it should be desired to modify the normal taper in the sections to make it conform more closely to some desired overall taper, it can be done by introducing appropriate changes in the lead screw settings.

In referring to lead screw settings here and elsewhere, we have in mind the particular wire pulling mechanism which is shown and described herein. It will be understood, however, that any other suitable wire pulling mechanisms can be used, so long as it includes some device by means of which different wire speedsmay be obtained as required.

' The electrolytic cell system has been fully described anda certain amount of explanation as to its operation has been made. A few supplementary remarks may be helpful nevertheless.

Referring to Fig. 11, when the wire I52 leaves the cathode section ll, it pulls a certain amount of electrolyte along which drains into compartment 48. The wire is wet with the electrolyte, however, as'it enters the washing compartment '56. Here the electrolyte-is thoroughly washed off, a good circulation of wash water being maintained. The water also wets the wire but is squeezed'ofi as the wire enters the mercury compartment 59, together with a trace of electrolyte that may remain.

Thus the transfer of any substantial amount of electrolyte to the mercury compartment is prevented. Notwithstanding this, it is found that if the wash water is supplied directly to the washing compartment, the mercury will become dirty after a time and lose a part of its surface tension. Whether this is due to exposure to the air or to a slight contamination with electrolyte or to some other cause is not certain, but it is known that'all trouble from this source is eliminated by introducing the wash water into the mercury compartment, whence it overflows into the washing compartment. Thi arrangement keeps the mercury clean and bright;

It will not'be necessary to go into the details of the electro-chemical action which takes place, it being known that with an electrolyte of the type disclosed herein the flow of the electric current will cause the removal of metal from certain metallic anodes,'-the' metal removed forming soluble salts. Generally speaking, this is what takes place in the apparatus described,

when tapering wire made from the alloy previouslyreferred to herein It may be mentioned that the iron in'the alloy tends to plate out on the cathode-tosome extent. This does no harm. An'objectionable' feature, however, is that the silicon forms an insoluble compound, aform of water glass, which after atime tends to clog the passages for the flow of electrolyte through the cells. This objection is not serious and can be overcome by the installation 'of a" filter, preferably inthe'pipe connection which returns the electrolyte from the collecting trough to the main tank When the current is firstturned on, it is substantially equally divided-between the individual electrolytic cells. This'isto be expected because the current divides in accordancewiththe, resistance ofthe cells andthe cells are all alike and have approximately the same resistance.

enemas-2 A -.substantial part of the total resistance of each cell, however, is the resistance of the wire itself. The result is that as the operation proceeds and the wire in the apparatus becomes tapered, the resistances of the several cells do .not remain the same, but begin to increase in accordance with the increasing wire resistance at such cells. The wire in the apparatus becomes tapered from left to right, that is, the entering wire at the left always has the same original diameter, while the emerging wire at the right becomes progressively smaller, and accordingly the increase in cell resistance is progressive from left to right, being a maximum in the last cell.

shift takes place as the tapering operation proneeds, the current progressively decreasing in the cells toward the right and progressively increasing in the cells toward the left of the cen- .ter of the apparatus. The current shift corresponds to the taper on the wire in the apparatus at any instant but is not proportionate in extent or amount because the wire resistance at any cell constitutes only a part of its total resistance, the remaining resistance being independent of the size of the wire. that the amount of current shift is consider-- ably less than would be expected from a consideration of the difference between the size of the wire at the entering end and its size at the emerging end of the apparatus. in the manufacture of the tapered wire previously referred to herein, which tapers from a larger diameter of 4.9 mils to a smaller diameter of 1.4 mils, the current in the last cell drops from an initial value of about .8 ampere to a final value of about .28 ampere. The final value is therefore about one third the initial value. At the first cell the current rises from an initial value of about .8 ampere to a final value of about 1.3 amperes.

The shift in the current toward the entering end of the apparatus affects the current density somewhat. At the start of a tapering operation the current density is approximately the same at all the cells. At the end of the operation there is an overall increase in the current density, due to the current being maintained constant and to the reduction of the area of wire in the apparatus which is exposed to the electrolyte. This increase is distributed between the several cells in accordance with the current they carry and the area of the wire in the electrolyte, and is a maximum at the first cell. At the last cell the increase is very small and the current density may be considered as remaining substantially constant, the decrease in the size of the wire just about compensating for the decrease in the current. If the wire is being reduced to a smaller diameter than 1.4 mils the current density in the last cell may decrease slightly toward the end of the operation but not enough to interfere with the production of a satisfactory smooth finish on the wire.

The shift in the current toward the entering end of the apparatus also affects the amount of work done at the several cells in removing metal from the wire, the amount of metal removed being proportional to the current. At the start the several cells do equal amounts of work, but as the tapering of a wire proceeds, a shift in the work takes place which corresponds to the cur- It follows For example,

:rent .shi-ft. This work-shift modifies $1162QQ81fition somewhat, but it does :not appear ;-to greatly affect the calculations of wire speeds based on the amount of metal to .be removed at the several sections.

It has been observed that there is no very sharp demarcation between the end :of the tapered section and the following cylinzdrical section, the corner being slightly rounded off, so to speak. This effect has been attributed to the work shift. It is generally advantageous rather than otherwise, but can be corrected if desired by a change in wire speed.

It will be understood that in setting the apparatus up for the manufacture of any particular tapered wire, the first few lots of wire made should ;be carefully tested to ascertain how closely they conform to the requirements, and appropriate adjustment of the wire speeds should Joe :made if found to be necessary. No adjust.-

.ation.

The apparatus described herein may also be used to manufacture very fine-wire which cannot be made by the usual drawing operations. In this connection it may be explained that the smallest wire which it is practicable to make by drawing is about 2 mils in diameter. Smaller wire can be made but only at a great expense. By means of the present invention wire havin .a diameter of about 2 mils or more, such as can be readily made by drawing, can readily be reduced to any desired smaller diameter down to .1 mil or less by pulling it through the apparatus at -.a constant speed. The first few feet :of wire, depending on tle length of the apparatus, will of course be tapered but the remainder will be of un-i forni cross section. The wire speed "will depend on the amount of reduction which is to take place, and can be calculated or determined experimentally.

.In the foregoing considerable amount of .specific information has been given as to the construction of the apparatus and the method of operating the same; but it will be understood that this has been done to facilitate the explanation of the principles involved and to afford information as to one way in which they may be employed in the successful practice of the invention. Without departure from these principles, numerous variations and modifications may be made, both as to the apparatus and the method of procedure and we do not, therefore, wish to be limited to the exact disclosure herein, but desire to include and have protected all forms and modifications of the invention which come within the scope of the appended claims.

We claim:

1. As an article of manufacture, an integrally formed resistance wire comprising two substantially cylindrical sections of different diameters and a tapered section joining said cylindrical sections.

2. As an article of manufacture, an integrally formed resistance wire for a nonlinear potentiometer, comprising two cylindrical sections of different diameters, respectively, a tapered section joining said cylindrical sections. said tapered 

